High‐Efficiency Full‐Space Complex‐Amplitude Metasurfaces Enabled by a Bi‐Spectral Single‐Substrate‐Layer Meta‐Atom.

Full‐space metasurfaces have attracted significant interest due to their unprecedented abilities to tailor the electromagnetic wavefronts in both transmission and reflection half‐spaces. However, it remains difficult and challenging to achieve high‐efficiency complex‐amplitude modulation within a single‐substrate‐layer structure for circularly polarized (CP) waves, which can enhance the power distribution regulation. Herein, a universal design strategy for the frequency‐multiplexed full‐space meta‐device is proposed by employing a single‐substrate‐layer meta‐atom with complex‐amplitude modulations. The full‐space metasurface is composed of a subwavelength‐thickness substrate and two discrepant metallic layers, where a modified complementary split‐ring resonator and an electric field coupled resonator are selected to refract and reflect the CP incidences to the cross‐ and co‐polarized components at two distinct frequencies. Based on this emerging meta‐atom, a multifunctional bi‐spectral metasurface is designed and verified by both full‐wave simulations and experiments, which generates the quad‐vortex beam and the hologram in transmission and reflection modes, respectively. The proposed method employs a single‐substrate layer to maintain high efficiency, while incorporating the complex‐amplitude modulation, which has potential applications in imaging and communication systems. [ABSTRACT FROM AUTHOR]